Statement of the Technical Field
The invention relates generally to Electronic Article Surveillance (“EAS”) systems, and more particularly to methods and systems for adjusting aspects of the detection process responsive to varying conditions.
Description of the Related Art
EAS systems generally comprise an interrogation antenna for transmitting an electromagnetic signal into an interrogation zone, markers which respond in some known electromagnetic manner to the interrogation signal, an antenna for detecting the response of the marker, a signal analyzer for evaluating the signals produced by the detection antenna, and an alarm which indicates the presence of a marker in the interrogation zone. The alarm can then be the basis for initiating one or more appropriate responses depending upon the nature of the facility. Typically, the interrogation zone is in the vicinity of an exit from a facility such as a retail store. The markers can be attached to articles such as items of merchandise or inventory.
One type of EAS system utilizes Acousto-Magnetic (“AM”) markers. The general operation of an AM EAS system is described in U.S. Pat. Nos. 4,510,489 and 4,510,490, the disclosures of which are herein incorporated by reference. The detection of markers in an AM EAS system by pedestals placed at an exit is focused on detecting markers within the spacing of the pedestals. For example, a first pedestal will generally include a main antenna field directed toward a surveillance or detection zone located between the first pedestal and a second pedestal. When an exciter signal is applied at the first pedestal, it will generate an Electro-Magnetic (“EM”) field of sufficient intensity so as to excite markers within the surveillance or detection zone. Similarly, the second pedestal will generally include an antenna having a main antenna field directed toward the surveillance or detection zone (and toward the first pedestal). An exciter signal applied at the second pedestal will also generate an EM field with sufficient intensity so as to excite markers within the surveillance or detection zone. When a marker tag is excited in the surveillance or detection zone, it will generate an EM signal which can usually be detected by receiving the signal at the antennas associated with the first and second pedestal.